In Patent Documents 1 and 2, there is disclosed an optical module in which an interference optical system is configured on an SOI (Silicon On Insulator) substrate by use of a MEMS technology. These interference optical systems include a beam splitter, a movable mirror attached to an electrostatic actuator, and a fixed mirror, and these are formed by applying etching to a silicon layer and an insulating layer of an SOI substrate into arbitrary shapes.